An IDEA MODIS Aerosol Optical Depth (AOD) image (above) depicted elevated AOD values of 0.6 to 0.8 over parts of the Southeast US (especially the northern half of Georgia) on 29 March 2007. Smoke from recent fire activity was likely the main contributor, but some of the elevated AOD signal may also have been due to very high pollen counts in that region — pine tree pollen has been unusually high this Spring season due to abnormally dry conditions that have plagued much of the southeastern US. In addition, light winds and increasing boundary layer moisture were helping to create an environment favorable for particle pollution growth — GOES sounder total precipitable water values of 25-35 mm were becoming more common over that particular region (below).

A major outbreak of severe convection developed across the southern and central Plains states during the day on 28 March and 29 March 2007; large and long-lived thunderstorms produced widespread tornadoes (including fatal tornadoes in Texas and Oklahoma, and the first tornado-related fatality in Coloradosince 1960), large hail (up to 4.5 inches in diameter in Texas), and damaging winds (28 March SPC storm reports). An AWIPS image of the MODIS 11.0Âµm InfraRed (“IR window”) channel with overlays of cloud-to-ground lightning strikes and surface wind streamlines (above) shows the large density of lightning strikes (1587 negative strikes and 61 positive strikes in a 15-minute period) that was generally aligned along a cold frontal boundary that was moving eastward across the Texas panhandle region. If we examine the MODIS IR image without any overlays (below), we see that there were 2 examples of a subtle “warm trench” signature (a ring of warmer cloud top temperatures surrounding the coldest temperatures associated with the overshooting tops) — this satellite signature suggests that there may have been some compensating subsidence immediately surrounding the vigorous overshooting tops as they penetrated the tropopause level. You can get a sense that such a â€œtrenchâ€ can surround an overshooting top by examining astronaut photography of thunderstorms taken from the space shuttle(image courtesy of Earth Sciences and Image Analysis Laboratory, NASA Johnson Space Center). QuickTime animations of rapid-scan GOES-11 10.7Âµm IR images centered on Lubbock, Texas and Goodland, Kansas show large and persistent enhanced-v signatures exhibited by many of these storms.